#include <bits/stdc++.h>
using namespace std;

#define ll long long
#define rep(i, n) for (int i = 0; i < (n); i++)
#define P pair<int, int>
#define LP pair<ll, ll>

template<class T>
void chmax(T& a, T b) { a = max(a, b); };
template<class T>
void chmin(T& a, T b) { a = min(a, b); };

int main() {
  int n, k;
  cin >> n >> k;
  vector<ll> x(n+2),a(n+1);
  rep(i,n) cin >> x[i+1];
  rep(i,n) cin >> a[i+1];
  const ll INF = 1e18;
  x[0] = -INF, x[n+1] = INF;
  ll l = x[k]-a[k], r = x[k]+a[k];
  int m = k, M = k;
  while (true) {
    int nxt1 = lower_bound(x.begin(),x.end(),l)-x.begin();
    int nxt2 = upper_bound(x.begin(),x.end(),r)-x.begin();
    nxt2--;
    if (nxt1==m&&nxt2==M) break;
    for (int i = m; i >= nxt1; i--) {
      chmin(l, x[i]-a[i]);
      chmax(r, x[i]+a[i]);
    }
    for (int i = M; i <= nxt2; i++) {
      chmin(l, x[i]-a[i]);
      chmax(r, x[i]+a[i]);
    }

    m = nxt1;
    M = nxt2;
  }
  int ans = M-m+1;
  cout << ans << endl;


  return 0;
}